1. Field of the Invention
The present invention relates to a high frequency module mainly used for a high frequency mobile communication machine such as a cellular phone and PDA (Personal Digital Assistant).
2. Description of the Related Technology
Conventionally, in a high frequency module using an LTCC (Low Temperature Co-fired Ceramic) substrate, a dielectric passive circuit such as a filter is generally formed only within the LTCC substrate. For example, a configuration example of high frequency module when a bandpass type filter formed by an equivalent circuit shown in FIG. 7 is formed within an LTCC substrate is as shown in FIG. 8.
The equivalent circuit shown in FIG. 7 is a bandpass type filter, and two LC resonance circuits are connected between an input terminal P1 and an output terminal P2 by coupling capacitors C1 to C3. One LC resonance circuit is formed by serially connecting an inductor RL1 and a capacitor RC1, and one end of the inductor RL1 is connected to the coupling capacitors C1, C2 and the other end of the capacitor RC1 is grounded. The other LC resonance circuit is formed by serially connecting an inductor RL2 and a capacitor RC2, and one end of the inductor RL2 is connected to the coupling capacitors C2 and C3 and the other end of the capacitor RC2 is grounded.
Further, a high frequency module 30 shown in FIG. 8 includes an LTCC substrate 33 on which electronic parts 31, 32 are mounted, and a bandpass type filter circuit 34 is formed within the LTCC substrate 33.
Furthermore, when it is necessary to prevent the interference with other lines, sometimes GND (ground) electrodes 44 are formed within the LTCC substrate 33 as in a high frequency module 30A shown in FIG. 9, and a passive circuit formed in an inner layer is shielded to the electronic parts 31, 32 and power supply lines (not shown) mounted on the substrate 33 by the GND electrodes 44.
In FIG. 9, an input terminal P1 is formed by an electrode 41 and an output terminal P2 is formed by an electrode 42. Further, a capacitor C1 is formed by an inductor electrode 52 that is located with one end thereof facing an capacitor electrode 51, an inductor RLI is formed by the inductor electrode 52, and a capacitor RC1 is formed by a capacitor electrode 53 that is located facing the other end of the inductor electrode 52 and connected to the GND electrode 44 through a via conductor 43.
Furthermore, a part of a capacitor C2 is formed by a capacitor electrode 54 that is located facing the one end of the inductor electrode 52 and another part of the capacitor C2 is formed by a capacitor electrode 55 that is located facing one end of an inductor electrode 56 and connected to the capacitor electrode 54 through the via conductor 43. Moreover, an inductor RL2 is formed by the inductor electrode 56, and a capacitor RC2 is formed by a capacitor electrode 57 that is located facing the other end of the inductor electrode 56 and connected to the GND electrode 44 through the via conductor 43. Further, a capacitor C3 is formed by a capacitor electrode 58 that is located facing the one end of the inductor electrode 56 and connected to the electrode 42 through the via conductor 43.
On the other hand, when the above described passive circuit such as a filter is not formed in the inner layer of the LTCC substrate, as shown in FIG. 10, the passive circuit function such as a filter is realized by configuring the passive circuit such as a filter itself as a single piece of electronic part 61 and mounting the electronic part 61 with another electronic part 62 on an LTCC substrate 63.
As the above described high frequency module, for example, high frequency modules disclosed in JP-A-2005-243785, JP-A-2005-243787, JP-A-2005-244814, etc. are known.
However, regarding high frequency modules, demands of markets for downsizing, especially thinning of modules have been increased. A conventional high frequency module using a dielectric substrate such as an LTCC substrate has a structure in which surface mounted components are mounted on the substrate, and the height of the high frequency module is determined by the total of thicknesses of the substrate and the surface mounted components.
Accordingly, in order to fulfill the demand for shorter height of the high frequency module, it is necessary to thin both the dielectric substrate such as an LTCC substrate and the surface mounted components. In a dielectric passive circuit device such as a filter or balance filter having characteristics that depend on the thickness of dielectric material, securing of the characteristics with the thinning has become an issue. Further, due to spread of FC (Flip Chip) mounting of semiconductors and downsizing of chip parts for mounting, the surface mounted components have become shorter in height and securing of the characteristics of dielectric passive circuit device of type mounted on the substrate has become harder.
That is, as described above, since the dielectric passive circuit device such as a filter is configured only by a module substrate or surface mounted components, in a high frequency module that simultaneously requires both shorter height and downsizing, there have been problems that a stray effect occurs between the device and a shielding shield for suppressing the interference with other lines, and it becomes difficult to secure the dielectric material thickness for obtaining good characteristics in a distributed constant type circuit having characteristics on which the dielectric material thickness has an influence.
For example, in the conventional structure as shown in FIG. 9, the passive circuit such as a filter is formed only within the dielectric module substrate such as an LTCC substrate. In order to shorten the height of the high frequency module, it is necessary to thin the thicknesses of the surface mounted components and the substrate as much as possible, and inhibition in magnetic flux generated in the inner layer inductor and increase in stray capacitance occur because the distance to the GND shield for shielding the interference with power supply lines, bus lines becomes shorter due to thinning.